An electronic parking brake (hereinafter, abbreviated as an EPB) system is a parking brake system which is electronically controlled to automatically generate a parking braking force according to an EPB switch and a state (a stationary or driving state) of a vehicle.
The EPB system has a function which automatically applies a parking brake when a vehicle is stationary. Therefore, in a stationary state, even though a driver does not put the brake, the parking brake is not released. Further, when the vehicle starts to travel, if the driver presses an accelerator while the parking brake is locked, the parking brake is automatically released so that the vehicle travels without performing any action, which may enhance safety and convenience of the vehicle.
Recently, the EPB system is configured to be integrated with a caliper and an ECU provided for the EPB drives a motor to allow the caliper to apply a pressure to a wheel disk.
FIG. 1 illustrates a motor driving circuit for an EPB system of the related art.
The motor driving circuit illustrated in FIG. 1 is disclosed in Korean Unexamined Patent Application Publication No. 2013-0057883 (titled “a device for detecting an error of a motor, published on Jun. 3, 2013) and includes a motor driving unit DV which drives a motor M according to a control signal which is applied from an ECU and monitoring units MC1 and MC2 which monitor a state of the motor M.
In FIG. 1, the motor driving unit DV includes four transistors T1 to T4 which configure an H-bridge circuit and the four transistors are connected with corresponding resistors R1 to R4 in parallel, respectively. The four transistors T1 to T4 are correspondingly applied with motor driving signals (not illustrated) which are applied from the ECU to be turned on/off to apply a battery power BATT and a ground power Vss to two power input terminals of the motor M, thereby driving the motor.
A reverse-polarity protecting transistor F1 for reverse-polarity protection is connected between the battery power BATT and one terminal of the H-bridge circuit and an activating transistor F2 which activates the H-bridge circuit in response to a fail-safe control signal FSC which is applied from the ECU is connected between the other terminal of the H-bridge circuit and the ground power VSS.
In the meantime, two monitoring units MC1 and MC2 are connected to corresponding input terminals of two power input terminals of the motor M, respectively. The monitoring units MC1 and MC2 do not directly receive a power which is input to the motor, but distributes the power to have an appropriate voltage level for monitoring using three resistors (R11, R12, and R13) and (R21, R22, and R23) to output monitoring signals MON1 and MON2.
The motor driving circuit of FIG. 1 includes the monitoring units MC1 and MC2 to analyze the monitoring signal and detect whether the motor is open or whether to be short from the battery power BATT and the ground power Vss.
However, the motor driving circuit of FIG. 1 is configured such that the monitoring units MC1 and MC2 output the monitoring signals using the resistors (R11, R12, and R13) and (R21, R22, and R23) respectively. Therefore, two current paths P1 and P2 through which the battery power BATT is connected with the ground power Vss through the resistors R1 and R3 of the motor driving unit DV and the resistors R12, R13 and R22, R23 of the monitoring units MC1 and MC2 are generated. A unit for controlling a current is not provided on the current paths. Therefore, dark current which is not intended at the time of designing a motor driving circuit is generated. The dark current varies depending on a resistance of the resistors which are applied to the motor driving circuit, but the resistances of the resistors are generally several tens to several hundreds kΩ when considering a characteristic of the EPB system and thus the dark current may be 100 μA. However, this indicates dark current which is generated in one motor driving circuit. Therefore, the caliper integrated EPB in the vehicle drives two motors so that approximately 200 μA of dark current may be generated in the motor driving circuit for the EPB system in every vehicle.
The current which is consumed by the dark current uses current which is charged in a battery of the vehicle, so that even a small amount of consumed current may affect the driving of the vehicle in the future. Further, in the case of a rechargeable battery for a vehicle, when the current is continuously consumed by the dark current, the life span of the battery may be shortened. Therefore, the dark current must be reduced.